Casey Handmer packed a sonar transducer up to Tulainyo Lake at 3,921 meters in the Sierra Nevada—the highest alpine tarn in the contiguous US—and sounded its bathymetry from a packraft. The lake reaches a depth of 117 meters, making it a sheer-sided glacial kettle and the deepest lake on Earth relative to its 800-meter surface diameter. caseyhandmer.wordpress.com